mirror of
https://github.com/matrix-construct/construct
synced 2024-08-26 03:15:17 +02:00
66 lines
1.7 KiB
C++
66 lines
1.7 KiB
C++
// The Construct
|
|
//
|
|
// Copyright (C) The Construct Developers, Authors & Contributors
|
|
// Copyright (C) 2016-2020 Jason Volk <jason@zemos.net>
|
|
//
|
|
// Permission to use, copy, modify, and/or distribute this software for any
|
|
// purpose with or without fee is hereby granted, provided that the above
|
|
// copyright notice and this permission notice is present in all copies. The
|
|
// full license for this software is available in the LICENSE file.
|
|
|
|
#pragma once
|
|
#define HAVE_IRCD_SIMD_LZCNT_H
|
|
|
|
namespace ircd::simd
|
|
{
|
|
template<class T> uint lzcnt(const T) noexcept;
|
|
}
|
|
|
|
/// Convenience template. Unfortunately this drops to scalar until specific
|
|
/// targets and specializations are created.
|
|
template<class T>
|
|
inline uint
|
|
__attribute__((target("lzcnt")))
|
|
ircd::simd::lzcnt(const T a)
|
|
noexcept
|
|
{
|
|
// The behavior of lzcnt can differ among platforms; when true we expect
|
|
// lzcnt to fall back to bsr-like behavior.
|
|
constexpr auto bitscan
|
|
{
|
|
#ifdef __LZCNT__
|
|
false
|
|
#else
|
|
true
|
|
#endif
|
|
};
|
|
|
|
uint ret(0), i(0); do
|
|
{
|
|
const auto mask
|
|
{
|
|
boolmask(uint(ret == sizeof_lane<T>() * 8 * i))
|
|
};
|
|
|
|
if constexpr(bitscan && sizeof_lane<T>() <= sizeof(u16))
|
|
ret += (15 - __lzcnt16(__builtin_bswap16(a[i++]))) & mask;
|
|
|
|
else if constexpr(sizeof_lane<T>() <= sizeof(u16))
|
|
ret += __lzcnt16(__builtin_bswap16(a[i++])) & mask;
|
|
|
|
else if constexpr(bitscan && sizeof_lane<T>() <= sizeof(u32))
|
|
ret += (31 - __lzcnt32(__builtin_bswap32(a[i++]))) & mask;
|
|
|
|
else if constexpr(sizeof_lane<T>() <= sizeof(u32))
|
|
ret += __lzcnt32(__builtin_bswap32(a[i++])) & mask;
|
|
|
|
else if constexpr(bitscan)
|
|
ret += (63 - __lzcnt64(__builtin_bswap64(a[i++]))) & mask;
|
|
|
|
else
|
|
ret += __lzcnt64(__builtin_bswap64(a[i++])) & mask;
|
|
}
|
|
while(i < lanes<T>());
|
|
|
|
return ret;
|
|
}
|